You continue to just keep showing them that you are interested, and love what they do.............simple.
I told my son that one abstract painting my 3 yr old granddaughter had done was worthy to frame.
I told him it was gallery quality....So he bought a small gold gilded frame, and
hung the art work.
It was a stark white background, with black design.It looked wonderful!
So pick out something you can frame, even if it is only small....put in a nice frame and see your child's reaction.(make sure you hang it).
Dance is also encouraged with some nice music...or happy hip-hop kids music.Clap and dance along too...... you show you are very happy with your child, see how that child will be inspired to continue to do more.
It is All in the encouragement of a parent or parents.